Author Topic: 1926-1934 OHV exhaust pipe dimensions needed  (Read 4420 times)

0 Members and 1 Guest are viewing this topic.

Offline Doug

  • Administrator
  • ****
  • Join Date: Mar 2004
  • Posts: 4460
  • Location: Glen Mills, PA, USA
1926-1934 OHV exhaust pipe dimensions needed
« on: 29 Jul 2008 at 00:45 »
I have been working on a small batch of stainless steel exhaust pipes for the DT models and have run into a bit of a snag. There are a few factory drawings of the exhaust systems as fitted to the DT, OC, TT, and F/G31 models. These show that they all used the same horizontal and vertical offsets for the tubing bends. Really the only thing that changed was with the advent of the DT the introduction of port flanges instead of gland rings as used on the older models, and how much pipe stuck out the back.

Machining the rear collector, the white object in the upper left is the fixture.

So I based my pipes on these dimensions, figuring it would make the blanks compatible with the widest range of models; covering the large OHV machines from 1926 through 1934. But when fitting the first trial set to my SW chassis I discovered the horizontal run fouled the LH foot rest post. Assuming I had made an error along the way, I verified in turn my drawings, the virtual model on the computer, the original factory drawing, and finally the parts I had made. Checking the battered pipe that came off the SW, it did indeed measure with less ‘drop’ such that it would just pass over the foot rest post. It also sat in closer to the engine than the works drawing called for. Now the drawing for the DT pipe does not say it fits the SW model as well, and of course on a DT there is no LH foot rest post to get in the way. But this same pipe is used on the TT, OC, and F/G31, and they have foot rest posts on the LH side as so would face a similar problem as the SW.

Mock-up of engine in chassis to test fit parts of the exhaust.

I could see perhaps the 1926 OC models being exempt from this, as the catalog illustration shows it with the old style foot board mountings. I am not sure if these still used a foot rest post attached to the frame, or had some sort of clamp on bracket like the 600EW, that would have allowed the bracket to ‘sneak under’ the exhaust pipe. Be that as it may, the drawing for the OC pipes say they are for the ’27 OC, and that had foot rest posts so far as I know. Ditto the F/G31 models. And I know these latter OC and the F/G31 models had the foot rest post straight out from the centerline of the lower frame tube; no joggles or offsets to lower the foot rest post under the pipe. And as far as I know, all these engines sat about the same height in the frame. It was not till a crankcase redesign in 1935 that the engine was raised by some 3/4” (which would help clear any foot rest posts by a comfortable margin.)

Now raising the pipe and moving it in a little is not so bad. It means trimming a little more off the parts, and that is a lot easier to do than the opposite problem! The question is do I make them all SW pattern and let then sit a little high on DT, OC, TT and F/G31 applications? Or is there some hereditary error in the Works drawings and those offsets are not what they used in practice? So I am asking owners of OC, G/H28-29, TT26-28, DT, SW, F/G31-33, and 1934 OW/OW1 models with stock exhaust systems to take the measurements indicated below. Basically all the big OHV models from 1926-1934.

What I would like to know is the vertical and horizontal distance from the frame tube. In the vertical direction this is probably easier to measure A and B relative to a common reference such as level ground. The bike should be level too! I would also be interested to know the horizontal offset indicated by C, if possible.  Originally the pipes did tip up to the rear ever so slightly, the vertical offset of the front pipe dropping down 1-15/16”, and the vertical drop of the rear pipe being slightly less at 1-7/8”. Why I do not know, but the same dimensions kept coming up on drawing after drawing to preclude a mistake. As I said, these values put the pipe through the top of the LH foot rest post on my SW. I am hoping a survey of these models might shed some light on just what Kingwood were thinking.